1. Field of the Invention
The subject of the present invention is a rotor moulded of plastic material, intended for rotary installation in a cavity of a pump body and for reception of one or more vanes forming the pumping members. The vane pumps are widely used for pumping fluids, and for example they find particular applications in motor vehicles.
2. Related Art
To the rotor of a vane pump three operations are mainly required:
(1) Transmission of the motion. The rotor, which is driven in rotation within a chamber of the pump body, transmits the movement to the vane or the vanes of the pump. It undergoes sliding displacements against the surfaces of the pump body with respect to which it is made to rotate. The rotor is required not to undergo excessive wear and not to produce excessive friction during its sliding displacements.
(2) Guide for the vane or the vanes of the pump. The rotor guides the vane or the vanes which, during the operation, undergo sliding displacements against the guide parts of the rotor. The rotor is required not to undergo itself nor cause to the vanes a noticeable wear, and not to produce excessive friction.
(3) Seal of the fluids. The rotor is required to actuate an operation of seal to the air and the oil in correspondence to the mechanical clearances and, in particular, to the friction bearings and to the regions where the rotor is tangent to the wall of the chamber inside the pump body.
In order to be able to perform these different functions, these rotors have a relatively complicated shape and, therefore, it is suitable and customary that they are embodied by moulding a suitable plastic material. However, the rotors of plastic material have some disadvantages. The plastic material has not a high mechanical resistance, it is relatively subject to wear in the portions subject to gliding contact, it is subject to non negligible ageing phenomena, and it is considerably sensible to the changes in temperature, which are particularly severe in the applications to motor vehicles, where the pump is required to operate within a large temperature field from −40° C. to +150° C.
According to the known technique, these disadvantages may be partially overcome or reduced by having recourse to special complicated rotor shapes and to an increase of the cross sections thereof and therefore of the quantity of material used, and in any event it is unavoidable to accept a suitable limitation of the stresses undergone by the material, to which correspond some limitations of the possible rotor performances.